Atypical diffusion-weighted magnetic resonance findings in glioblastoma multiforme

Differentiating glioblastoma multiforme from cerebral lymphoma: application of advanced texture analysis of quantitative apparent diffusion coefficients

PURPOSE

The purpose of this study was to differentiate glioblastoma multiforme from primary central nervous system lymphoma using the customised first and second-order histogram features derived from apparent diffusion coefficients.Methods and materials: A total of 82 patients (57 with glioblastoma multiforme and 25 with primary central nervous system lymphoma) were included in this study. The axial T1 post-contrast and fluid-attenuated inversion recovery magnetic resonance images were used to delineate regions of interest for the tumour and peritumoral oedema. The regions of interest were then co-registered with the apparent diffusion coefficient maps, and the first and second-order histogram features were extracted and compared between glioblastoma multiforme and primary central nervous system lymphoma groups. Receiver operating characteristic curve analysis was performed to calculate a cut-off value and its sensitivity and specificity to differentiate glioblastoma multiforme from primary central nervous system lymphoma.

RESULTS

Based on the tumour regions of interest, apparent diffusion coefficient mean, maximum, median, uniformity and entropy were higher in the glioblastoma multiforme group than the primary central nervous system lymphoma group (P ≤ 0.001). The most sensitive first and second-order histogram feature to differentiate glioblastoma multiforme from primary central nervous system lymphoma was the maximum of 2.026 or less (95% confidence interval (CI) 75.1-99.9%), and the most specific first and second-order histogram feature was smoothness of 1.28 or greater (84.0% CI 70.9-92.8%). Based on the oedema regions of interest, most of the first and second-order histogram features were higher in the glioblastoma multiforme group compared to the primary central nervous system lymphoma group (P ≤ 0.015). The most sensitive first and second-order histogram feature to differentiate glioblastoma multiforme from primary central nervous system lymphoma was the 25th percentile of 0.675 or less (100% CI 83.2-100%) and the most specific first and second-order histogram feature was the median of 1.28 or less (85.9% CI 66.3-95.8%).

CONCLUSIONS

Texture analysis using first and second-order histogram features derived from apparent diffusion coefficient maps may be helpful in differentiating glioblastoma multiforme from primary central nervous system lymphoma.

Intracranial peripherally enhancing lesions in cardiac transplant recipients: A rare case series and literature review

Intracranial peripherally enhancing lesions in immunosuppressed solid organ transplant recipients represent a unique diagnostic and management dilemma due to the vast array of differentials that demand consideration. Diagnosis of the underlying pathology is often guided by the use of magnetic resonance imaging (MRI). We present the first published case series of three cardiac transplant recipients with significantly atypical neuroradiological findings contrary to the tenets of contemporary literature. Our rare case series consists of: (1) A sterile Mycobacterium pyogenic abscess mimicking glioblastoma multiforme due to an immunosuppressed state (2) Epstein Barr Virus encephalitis masquerading as Central Nervous System Post-Transplant Lymphoproliferative Disorder (3) An unusual case of partially treated disseminated Nocardiosis warning of the need to consider the immunosuppressed state and partial treatment response obfuscating classical MRI appearances. We utilise these unprecedented cases as the basis of a literature review to understand the pathophysiology behind the peculiar imaging findings in this rarefied cohort of transplant recipients, and rationalise why the MRI findings in each instance contradicts the accepted imaging patterns. In the setting of potential unreliability of neuroradiology in this immunosuppressed unique subgroup, we hope to impart to clinicians that definitive diagnosis obtained by emergent neurosurgical intervention may be necessary to accurately and expediently guide further medical management.

Comparison between MRI-derived ADC maps and 18FLT-PET in pre-operative glioblastoma

BACKGROUND AND PURPOSE

Among principal MRI sequences used for a better pre-therapeutic characterization of glioblastoma (GBM), DWI-derived ADC is expected to be a good parameter for the evaluation of cellularity, due to restricted water diffusivity. We aimed here to compare ADC maps to ¹⁸FLT-PET, a proliferation tracer, in GBM cases.

MATERIALS AND METHODS

Patients underwent ¹⁸FLT-PET, followed by multiparametric magnetic resonance imaging (MRI) just prior to surgery. We analysed in this study twenty GBM confirmed patients. The 5th percentile (5p) of the ADC values were thresholded to define the ADC_min ROI, while the 95th percentile (95p) of the SUV FLT values were used to define the FLT_max ROI. The statistical and spatial correlations between these two groups of ROIs were analyzed.

RESULTS

We did not observe any significant correlations between ADC_min and FLT_max cut-off values (R²=0.0285), neither between ADC_min and FLT_max ROIs (mean Dice=0.09±0.12). Mean ADC values in the FLT_max defined ROI were significantly higher than the values in the ADC_min ROI (P<0.001). Mean FLT values in the FLT_max ROI were significantly higher than the values in the ADC_min ROI (P<0.001).

CONCLUSIONS

When comparing ADC maps to ¹⁸FLT uptake, we did not observe significant anatomical overlap nor correlation, between the regions of low ADC and high FLT disabling to clearly link ADC values to cellular proliferation. The exact significance of ADC maps in GBM has yet to be elaborated.

Cerebral Metastases of Lung Cancer Mimicking Multiple Ischaemic Lesions - A Case Report and Review of Literature

Background

Restricted diffusion that is found on magnetic resonance diffusion-weighted imaging (DWI) typically indicates acute ischaemic stroke. However, restricted diffusion can also occur in other diseases, like metastatic brain tumours, which we describe in this case report.

Case Report

A 57-year-old male, with a diagnosis of small-cell cancer of the right lung (microcellular anaplastic carcinoma), was admitted with focal neurological symptoms. Initial brain MRI revealed multiple, disseminated lesions that were hyperintense on T2-weighted images and did not enhance after contrast administration; notably, some lesions manifested restricted diffusion on DWI images. Based on these findings, disseminated ischaemic lesions were diagnosed. On follow-up MRI that was performed after 2 weeks, we observed enlargement of the lesions; there were multiple, disseminated, sharply outlined, contrast-enhancing, oval foci with persistent restriction of diffusion. We diagnosed the lesions as disseminated brain metastases due to lung cancer. To our knowledge, this is the first description of a patient with brain metastases that were characterised by restricted diffusion and no contrast enhancement.

Conclusions

Multiple, disseminated brain lesions, that are characterised by restricted diffusion on DWI, typically indicate acute or hyperacute ischemic infarcts; however, they can also be due to hypercellular metastases, even if no contrast enhancement is observed. This latter possibility should be considered particularly in patients with cancer.

Differentiation between Glioblastoma Multiforme and Primary Cerebral Lymphoma: Additional Benefits of Quantitative Diffusion-Weighted MR Imaging

The differentiation between glioblastoma multiforme (GBM) and primary cerebral lymphoma (PCL) is important because the treatments are substantially different. The purpose of this article is to describe the MR imaging characteristics of GBM and PCL with emphasis on the quantitative ADC analysis in the tumor necrosis, the most strongly-enhanced tumor area, and the peritumoral edema. This retrospective cohort study collected 104 GBM (WHO grade IV) patients and 22 immune-competent PCL (diffuse large B cell lymphoma) patients. All these patients had pretreatment brain MR DWI and ADC imaging. Analysis of conventional MR imaging and quantitative ADC measurement including the tumor necrosis (ADCn), the most strongly-enhanced tumor area (ADCt), and the peritumoral edema (ADCe) were done. ROC analysis with optimal cut-off values and area-under-the ROC curve (AUC) was performed. For conventional MR imaging, there are statistical differences in tumor size, tumor location, tumor margin, and the presence of tumor necrosis between GBM and PCL. Quantitative ADC analysis shows that GBM tended to have significantly (P<0.05) higher ADC in the most strongly-enhanced area (ADCt) and lower ADC in the peritumoral edema (ADCe) as compared with PCL. Excellent AUC (0.94) with optimal sensitivity of 90% and specificity of 86% for differentiating between GBM and PCL was obtained by combination of ADC in the tumor necrosis (ADCn), the most strongly-enhanced tumor area (ADCt), and the peritumoral edema (ADCe). Besides, there are positive ADC gradients in the peritumoral edema in a subset of GBMs but not in the PCLs. Quantitative ADC analysis in these three areas can thus be implemented to improve diagnostic accuracy for these two brain tumor types. The histological correlation of the ADC difference deserves further investigation.

Diffusion-Weighted Magnetic Resonance Imaging and ADC Maps in the Diagnosis of Intracranial Cystic or Necrotic Lesions

This study evaluated the usefulness of diffusion-weighted (DW) magnetic resonance imaging (MRI) and ADC maps in the differential diagnosis of brain abscesses from cystic or necrotic neoplasms. MR images of 49 patients with 54 lesions were examined retrospectively. All patients underwent conventional MRI and DWI, and ADC values were calculated by placing ROIs of 30 mm2 manually over the cystic part of the lesions. On DWI, all cystic portions of abscesses were hyperintense. Mean ADC values were 0.48×10 mm2/s (range 0.41–0.54×10 mm/s) for pyogenic abscesses, 0.73×10 mm2/s (range 0.65–0.91×10 mm/s) for mycotic abscesses and 0.6 mm2/s for Nocardia abscess. Cystic areas appeared hypointense on DWI in 33/44 tumours (mean value ADC 1.96 mm2/s). Eleven tumours (11/44) appeared hyperintense on DWI: eight metastases from lung cancer (mean ADC value 0.86 mm2/s, range 0.75–1.2 mm2/s), two GBMs (mean 0.7 mm2/s, range 0.67–0.76 mm2/s) and one anaplastic astrocytoma (ADC value 1.24 mm2/s). ADC values may help in differentiating pyogenic abscess from brain tumors or metastatic lesions.

Hemorrhagic Cerebellar Abscess

BACKGROUND

Brain abscess represents a significant medical problem, accounting for 1 in every 10,000 U.S. hospital admissions and imposing a mortality of 17%-32%. Treatment success depends on early diagnosis, allowing for prompt intervention before a potentially catastrophic rupture. However, diagnosis can be difficult because currently no magnetic resonance imaging signal characteristics are pathognomonic. The presence of hemorrhage may further complicate the radiographic detection of an abscess, potentially leading to delayed treatment.

CLINICAL PRESENTATION

A 71-year-old man was diagnosed with hemorrhagic cerebellar abscess as a complication of groin abscess after cardiac catheterization. After surgical resection of the cerebellar abscess and culture-based antibiotic treatment, the patient suffered repeat hemorrhages into the abscess cavity, of which he died. We describe his clinical course with emphasis on radiology-based differential diagnosis. We also describe the possible pathogenesis of this rare case, based on review of the literature.

CONCLUSIONS

To our knowledge, this is the first report on recurrent hemorrhages in a cerebellar abscess. Hemorrhagic brain abscess has a complex radiologic appearance, which may delay diagnosis and treatment. A high degree of clinical suspicion is necessary to ensure timely treatment of this potentially lethal lesion.

Diffusion-weighted MRI in neuro-oncology

Diffusion-weighted MRI (DW-MRI) provides image contrast dependent on the molecular movement of water. It has been most widely used in the diagnosis of cytotoxic edema secondary to acute cerebral ischemia, but has also proven useful in assessing tumor cellularity and grade, abscess formation, cysts and various forms of white matter disorders. Furthermore, DW-MRI is used to generate maps of subcortical white matter tracts and their relationship to structural brain lesions that may serve for preoperative planning and intraoperative guidance. We provide a comprehensive review of current practical applications of DW-MRI in the diagnosis and treatment of primary brain tumors, metastases and nonmetastatic neurologic complications of cancer. A detailed description of diffusion tensor imaging is beyond the scope of this review. We performed a comprehensive search of the PubMed database of the USA National Library of Medicine with use of various combinations of the following search terms: diffusion-weighted imaging, apparent diffusion coefficient, diffusion tensor imaging, diffusion tensor, brain, tumor, glioblastoma, lymphoma, primary CNS lymphoma, stroke, cancer, abscess, leukoencephalopathy, methotrexate, fluorouracil, capecitabine. We identified original articles and well-documented case reports of DW-MRI applications in patients with primary brain neoplasms, metastases and nonmetastatic neurologic complications that we judged to be of high impact on the field. We largely selected publications from the past 10 years, but did not exclude commonly referenced and highly regarded older publications. We also searched the reference lists of articles identified by this search strategy and selected those we judged relevant. Review articles are cited to provide readers with more details and more references than can be covered here.

Differentiation between primary cerebral lymphoma and glioblastoma using the apparent diffusion coefficient: comparison of three different ROI methods

Objective

Apparent diffusion coefficients (ADC) can help differentiate between central nervous system (CNS) lymphoma and Glioblastoma (GBM). However, overlap between ADCs for GBM and lymphoma have been reported because of various region of interest (ROI) methods. Our aim is to explore ROI method to provide the most reproducible results for differentiation.

Materials and Methods

We studied 25 CNS lymphomas and 62 GBMs with three ROI methods: (1) ROI₁, whole tumor volume; (2) ROI₂, multiple ROIs; and (3) ROI₃, a single ROI. Interobserver variability of two readers for each method was analyzed by intraclass correlation(ICC). ADCs were compared between GBM and lymphoma, using two-sample t-test. The discriminative ability was determined by ROC analysis.

Results

ADCs from ROI₁ showed most reproducible results (ICC >0.9). For ROI₁, ADC_mean for lymphoma showed significantly lower values than GBM (p = 0.03). The optimal cut-off value was 0.98×10⁻³ mm²/s with 85% sensitivity and 90% specificity. For ROI₂, ADC_min for lymphoma was significantly lower than GBM (p = 0.02). The cut-off value was 0.69×10⁻³ mm²/s with 87% sensitivity and 88% specificity.

Conclusion

ADC values were significantly dependent on ROI method. ADCs from the whole tumor volume had the most reproducible results. ADC_mean from the whole tumor volume may aid in differentiating between lymphoma and GBM. However, multi-modal imaging approaches are recommended than ADC alone for differentiation.

Advanced MR imaging of gliomas: an update

Recent advances in the treatment of cerebral gliomas have increased the demands on noninvasive neuroimaging for the diagnosis, therapeutic planning, tumor monitoring, and patient outcome prediction. In the meantime, improved magnetic resonance (MR) imaging techniques have shown much potentials in evaluating the key pathological features of the gliomas, including cellularity, invasiveness, mitotic activity, angiogenesis, and necrosis, hence, further shedding light on glioma grading before treatment. In this paper, an update of advanced MR imaging techniques is reviewed, and their potential roles as biomarkers of tumor grading are discussed.

Diffusion MR Imaging of the Brain in Patients with Cancer

Over the last several years, there has been significant advancement in the molecular characterization of intracranial diseases, particularly cerebral neoplasms. While nuclear medicine technology, including PET/CT, has been at the foreground of exploration, new MR imaging techniques, specifically diffusion-weighted and diffusion tensor imaging, have shown interesting applications towards advancing our understanding of cancer involving the brain. In this paper, we review the fundamentals and basic physics of these techniques, and their applications to patient care for both general diagnostic use and in answering specific questions in selection of patients in terms of expected response to treatment.

Pyogenic abscess from Providencia stuartii mimicking necrotic tumour at perfusion-weighted imaging

The purpose of this case report is to increase the knowledge about magnetic resonance spectrum of pyogenic abscesses of the brain. A 74-year-old woman presented with a left frontal lobe cystic mass, developed in the site of post-traumatic contusions after surgical evacuation of a subdural hematoma. MR imaging showed an ipsilateral mass lesion with a thin, regular rim of T1 high-intensity signal, T2 low-intensity signal, and gadolinium-enhancement. Diffusion-weighted imaging with measure of apparent diffusion coefficient value showed inhomogenous diffusion restriction in the lesion core. Perfusion-weighted imaging (PWI) demonstrated high relative cerebral blood volume (rCBV) in both the lesion wall and perilesional area, with a maximal rCBV ratio (rCBV of the lesion/rCBV of the normal contralateral white matter) of 5.65 and 0.58, respectively. As a result, surgery and pathology showed a pyogenic abscess. Cultures grew were Providencia stuartii species. In conclusion, a pyogenic brain abscess from P. stuartii may show high rCBV at PWI, thus mimicking a necrotic tumour.

Differentiation between glioblastomas, solitary brain metastases, and primary cerebral lymphomas using diffusion tensor and dynamic susceptibility contrast-enhanced MR imaging

BACKGROUND AND PURPOSE

Glioblastomas, brain metastases, and PCLs may have similar enhancement patterns on MR imaging, making the differential diagnosis difficult or even impossible. The purpose of this study was to determine whether a combination of DTI and DSC can assist in the differentiation of glioblastomas, solitary brain metastases, and PCLs.

MATERIALS AND METHODS

Twenty-six glioblastomas, 25 brain metastases, and 16 PCLs were retrospectively identified. DTI metrics, including FA, ADC, CL, CP, CS, and rCBV were measured from the enhancing, immediate peritumoral and distant peritumoral regions. A 2-level decision tree was designed, and a multivariate logistic regression analysis was used at each level to determine the best model for classification.

RESULTS

From the enhancing region, significantly elevated FA, CL, and CP and decreased CS values were observed in glioblastomas compared with brain metastases and PCLs (P < .001), whereas ADC, rCBV, and rCBV(max) values of glioblastomas were significantly higher than those of PCLs (P < .01). The best model to distinguish glioblastomas from nonglioblastomas consisted of ADC, CS (or FA) from the enhancing region, and rCBV from the immediate peritumoral region, resulting in AUC = 0.938. The best predictor to differentiate PCLs from brain metastases comprised ADC from the enhancing region and CP from the immediate peritumoral region with AUC = 0.909.

CONCLUSIONS

The combination of DTI metrics and rCBV measurement can help in the differentiation of glioblastomas from brain metastases and PCLs.

The role of diffusion-weighted magnetic resonance imaging in intracranial cystic lesions

We aimed to define the diffusion-weighted magnetic resonance (MR) imaging features of intracranial cystic lesions and to investigate possible special features for the differential diagnosis. One hundred and twenty patients with intracranial cystic lesions were included in the study. There were 29 arachnoid cysts, eight epidermoid cysts, 34 primary tumors, 18 abscesses, 29 metastases and two hydatid cysts. Echo-planar diffusion-weighted MR imaging was obtained in addition to conventional cranial MR scans. The morphologic features of the cystic portion and the wall of the cyst and signal intensities on diffusion-weighted images were evaluated. All abscesses and epidermoid cysts were hyperintense on diffusion-weighted images. Arachnoid cysts, hydatid cysts, primary tumors, and metastases were hypointense except five cystic tumors. These five primary or metastatic necrotic tumors showed high signal intensity on diffusion-weighted images due to hemorrhage or superinfection. The walls of the cystic tumors were usually hyperintense on diffusion-weighted images in contrast to the wall of the abscesses, which were iso-hypointense. This was a statistically significant finding for the differentiation between tumors and abscesses (p<0.05). Diffusion-weighted MR imaging is a useful technique for the evaluation of the intracranial cystic lesions and provides additional beneficial information to conventional MR imaging. However, the presence of hemorrhage and superinfection of the tumors may cause a signal increase that results in misinterpretetations. In these cases, the appearance of tumor wall may be useful for differentiating abscesses from tumors.

Cerebral abscesses and necrotic cerebral tumours: differential diagnosis by perfusion-weighted magnetic resonance imaging

PURPOSE

This study was undertaken to evaluate the usefulness of perfusion-weighted imaging (PWI) in the differential diagnosis of ring-enhancing cerebral lesions, including abscesses, high-grade gliomas and metastases.

MATERIALS AND METHODS

Nine cerebral abscesses (five pyogenic, four from Toxoplasma gondii), ten glioblastomas and five cerebral metastases in 19 patients were studied with gadolinium-enhanced magnetic resonance imaging, diffusion-weighted imaging (DWI) including calculation of mean apparent diffusion coefficient (ADC) of the lesion core, and PWI. At PWI, the mean of the maximum regional cerebral blood volume (rCBV) was calculated in the gadolinium-enhancing peripheral solid areas and compared with that of the contralateral normal-appearing white matter [ratio=rCBV (lesion)/rCBV (contralateral normal-appearing white matter)].

RESULTS

DWI achieved the differential diagnosis in all cases except for the four Toxoplasma abscesses. At PWI, the mean ratio of the rCBV of the capsular portion was 0.72+/-0.08 (range 0.60-0.82) in the pyogenic abscesses, 0.84+/-0.07 (range 0.75-0.91) in the Toxoplasma abscesses, 4.45+/-1.5 (range 2.9-8.0) in the high-grade gliomas and 3.58+/-0.68 (range 3.28-4.27) in the metastases.

CONCLUSIONS

PWI seems to be useful in the differential diagnosis of ring-enhancing cerebral lesions. High rCBV values in the peripheral areas appear to indicate the possibility of a necrotic tumour, whereas low values tend to indicate an abscess.

Primary cerebral lymphoma and glioblastoma multiforme: differences in diffusion characteristics evaluated with diffusion tensor imaging

BACKGROUND AND PURPOSE

Differentiating between primary cerebral lymphoma and glioblastoma multiforme (GBM) based on conventional MR imaging sequences may be impossible. Our hypothesis was that there are significant differences in fractional anisotropy (FA) and apparent diffusion coefficient (ADC) between lymphoma and GBM, which will allow for differentiation between them.

MATERIALS AND METHODS

Preoperative diffusion tensor imaging (DTI) was performed in 10 patients with lymphoma and 10 patients with GBM. Regions of interest were placed in only solid-enhancing tumor areas and the contralateral normal-appearing white matter (NAWM) to measure the FA and ADC values. The differences in FA and ADC between lymphoma and GBM, as well as between solid-enhancing areas of each tumor type and contralateral NAWM, were analyzed statistically. Cutoff values of FA, FA ratio, ADC, and ADC ratio for distinguishing lymphomas from GBMs were determined by receiver operating characteristic curve analysis.

RESULTS

FA and ADC values of lymphoma were significantly decreased compared with NAWM. Mean FA, FA ratio, ADC (x10(-3) mm(2)/s), and ADC ratios were 0.140 +/- 0.024, 0.25 +/- 0.04, 0.630 +/- 0.155, and 0.83 +/- 0.14 for lymphoma, respectively, and 0.229 +/- 0.069, 0.40 +/- 0.12, 0.963 +/- 0.119, and 1.26 +/- 0.13 for GBM, respectively. All of the values were significantly different between lymphomas and GBM. Cutoff values to differentiate lymphomas from GBM were 0.192 for FA, 0.33 for FA ratio, 0.818 for ADC, and 1.06 for ADC ratio.

CONCLUSIONS

The FA and ADC of primary cerebral lymphoma were significantly lower than those of GBM. DTI is able to differentiate lymphomas from GBM.

Diffusion MRI in the early diagnosis of malignant glioma

OBJECTIVE

A subset of patients with malignant glioma comes to medical attention before their masses show rim enhancement and central necrosis. Tumors in those cases are frequently located in eloquent areas of the brain. Tissue diagnosis is limited to stereotactic biopsy providing limited material for accurate grading. We conducted this study to determine whether imaging characteristics of early stages of malignant gliomas could aid in timely definitive diagnosis.

METHODS

We retrospectively analyzed patients with newly diagnosed malignant glioma seen at the Yale Brain Tumor Center between 2002 and 2005. Patients with typical radiographic presentation were excluded.

RESULTS

Of 89 patients, eight meeting the inclusion criteria were identified. In five patients, patchy or small nodular enhancing lesions without central necrosis were present within the tumor mass. Diffusion-weighted imaging (DWI) showed areas of increased signal intensity in all cases. Apparent diffusion coefficient maps (ADC) revealed low-signal intensity in corresponding areas. At the time of imaging, biopsy was performed in seven patients but diagnosis of malignant glioma could only be established prior to further tumor growth in four cases.

CONCLUSIONS

The diagnosis in the early stages of malignant glioma can be challenging in a subset of cases. Information obtained through DWI should be incorporated in the clinical decision-making process. Mass lesions displaying decreased water diffusion indicating high cellularity, are suggestive of a high-grade glioma. Biopsies are recommended. However, even when biopsies are inconclusive, a strong suspicion of malignant glioma should be considered.

Glioblastoma multiforme with diffusion-weighted magnetic resonance imaging characteristics mimicking primary brain lymphoma

✓ The authors report on the first case of corpus callosum glioblastoma multiforme (GBM) with diffusion-weighted (DW) magnetic resonance (MR) imaging findings that mimicked those for lymphoma but with MR spectroscopy results absent of lymphoma characteristics. This 68-year-old man presented with rapid, progressive impairment in short-term memory as well as slow responses and a change in his personality within 3 weeks of admission. Results of cranial computed tomography revealed a slightly hyperdense corpus callosum tumor with bihemispheric involvement. Magnetic resonance images showed a homogeneous mass with strong enhancement. The mass showed water restriction on DW MR images and apparent diffusion coefficient (ADC) maps but no markedly elevated lipid resonance on MR spectroscopy. The patient underwent tumor resection. Results of pathological studies with immunohistochemical analysis confirmed that the lesion was GBM.

Diffusion-weighted MR imaging together with ADC mapping and MR spectroscopy was reported to be useful in differentiating GBM and primary brain lymphoma. The lymphomas were hyperintense to gray matter on DW MR images and isointense to hypointense on ADC maps because of water restriction. In contrast, the GBMs were hyperintense to gray matter on both DW MR images and ADC maps because of the T2 shine-through effect. On MR spectroscopy, lipid resonance was markedly elevated in lymphoma but only slightly elevated in GBM.

Glioblastoma multiforme with atypical diffusion-weighted MR findings

The aim of this study is to review the diffusion-weighted MRI findings of glioblastomas, to investigate those with atypical characteristics and to emphasise the reasons responsible for the atypical features on diffusion-weighted MR images. 48 cases of histologically proven glioblastomas were included in this study. In addition to conventional sequences of routine tumour protocol, diffusion-weighted MRI with spin-echo echo-planar sequence was performed. The cystic-necrotic components of the lesions, according to the conventional sequences, were determined on the diffusion-weighted MR images and were classified as typical or atypical. The presence of high signal intensity was accepted as an atypical feature while low signal intensity was accepted as typical. The apparent diffusion coefficient (ADC) values of the cystic components were calculated. The statistical significance of the typical and atypical glioblastomas was evaluated with the students t-test. In six of the cases apparent high signal intensity in diffusion weighted MR images was interpreted. In three cases the high signal intensity occupied all of the cystic component and in the other three most of the cystic component. The ADC values of the lesions varied between 0.86 x 10(-3) mm(2) s(-1) and 1.39 x 10(-3) mm(2) s(-1) (mean value 1.06+/-0.17 x 10(-3) mm(2) s(-1)). In 42 of the lesions the cystic-necrotic component demonstrated low signal intensity and the ADC values varied between 1.56 x 10(-3) mm(2) s(-1) and 3.32 x 10(-3) mm(2) s(-1) (mean value 2.36+/-0.46 x 10(-3) mm(2) s(-1)). The difference between ADC values of atypical and typical lesions was statistically significant (p<0.001). The vast majority of glioblastomas do not exhibit restricted diffusion in diffusion-weighted MRI, but some of them display homogeneous or heterogeneous high signal intensity and decrease of ADC values. Diffusion-weighted MRI alone is not helpful in the differentiation of malignant tumours from abscesses with low ADC values and similar conventional MRI findings.